The invention relates to a method for obtaining a base material for building mortar, such as concrete-or masonry mortar and the like, this base material containing a sand fraction.
The invention relates particularly to the processing of base materials in large quantities, that is, in bulk quantities. It is usual to transport the base materials for the concrete industry, and specifically the sand used in the industry, from the extraction location to the place of use by inland waterway vessel. The concrete manufacturer or other user will separate out a small quantity of sand on the spot from the quantity supplied and mix it with cement and other aggregates in order to obtain the required concrete or masonry mortar. The drawback to such a method is that the aggregates have to be stored separately on the premises of the user, which, especially with substances having puzzolanic properties, that is the substance hardens under the influence of lime and moisture, is problematic with respect to storage costs and the attaining of the required percentage of aggregate.
The invention has for its object to provide a method whereby the above mentioned drawbacks are obviated, and the method is distinguished as such by:
the extraction at an extraction location and the separating out at a refining location of a quantity of sand with a granular size and distribution ratio lying within predetermined boundaries,
the subjecting of this quantity of sand to a moisturing or dewatering treatment until a moisture content of a maximum of 15% m/m is attained,
the supplying and/or storing in bulk of an aggregate with a smaller granular size than that of the sand fraction,
the dosed feeding and mixing of the sand fraction and aggregate by means of a through-flow process, the mixture obtained being poured or delivered in bulk as the required base material.
The invention is based on the idea of pre-treating the sand obtained at an extraction location in order to be able to provide the required base material already mixed in bulk to the end consumer. In view of the fact that the sand in a particular extraction location has a determined median granular size, the total grain size distribution ratio of the mix can be controlled better by the addition of an aggregate with a smaller granular size. As the starting point for the final concrete or masonry mortar, the base material is therefore of higher quality as a result of this more favourable grain size distribution ratio. The consumer is moreover no longer burdened with mixing aggregates himself, but purchases an already adapted base material of pre-determined homogeneous composition, conforming to the current NEN or international norms. Transportation of the sand fraction and aggregates can be carried out in bulk, which results in cost saving.
The invention proposes as a suitable aggregate the use of fly ash from for example electricity power stations. The aggregate, fly ash, can be provided in bulk from such large scale concerns, so that it can be mixed with the sand fraction that is present in bulk in an effective manner.
The use of fly ash in the mix provides the advantage that in the manufacture of concrete a part of the cement fraction can be substituted. It has been found in experiments that the substitution of 15% by weight of cement by fly ash, that is, approximately 5% by weight relative to sand, produces a quality of concrete with a final strength comparable to or higher than that of concrete with an unchanged content of cement. During setting there is a lower hydration heat because of the smaller quantity of cement in the concrete, such concrete moreover having a better resistance to sulphate corrosion as well as a lower permeability to aggressive liquids and gases.
The invention will be further elucidated in the following figure description of an embodiment.